Layered system with an electrically activatable layer

ABSTRACT

An electronic component has electrically activatable layer, e.g. in electroluminescent layer of porous silicon on a body of which two multiarthogonal grids are buried. A conductive layer on the electrically activatable layer forms a drain and another conductor forms the source, the grid bars being independently energizable to form current channels through the electrically activatable layer.

CROSS REFERENCE TO RELATED APPLICATION

This application is a national phase of PCT/DE 94/00383 filed 2 Apr.1994 and based, in turn, on German national application P 43 11388.5 of7 Apr. 1993 under the International Convention.

FIELD OF THE INVENTION

The invention relates to a layered system, especially for use in themicroelectronics or microtechnology fields, having an electricallyactivatable layer which has at least one contact electrode extendingover and connected to at least a part of a layer surface of the firstlayer side.

BACKGROUND OF THE INVENTION

Such a layer system is known from IEEE electron device letters, volume12, number 12, December 1991, pages 691-692. In part this deals with alayered system with a porous silicon layer having on its upper layerside a gold contact electrode extending over the layer surface andconnected thereto, the gold contact electrode having a thickness of 12nm. On the second layer side, the porous silicon layer is connected witha silicon wafer which has on its other (back) side a further goldcontact in the form of a 300 nm thick layer. Upon application of asufficient voltage or by passage of a sufficient electric currentbetween the two electrodes, an electroluminescence can be observed inthe porous silicon layer such that light emission is visible through the12 nm thick gold layer. For improved emission, this gold contact can bestructured with openings A drawback of this known layered system is,however, that the electrical activation of the porous silicon layer,because of the large-area contact electrodes both on the upper surfaceof this layer and on the underside of the silicon layer, allows only alarge-area electrical activation in the layer.

OBJECT OF THE INVENTION

It is an object of the present invention to provide a layered system ofthe aforedescribed type in which the electrically-activatable layer iscontrollable in a laterally-limited manner.

SUMMARY OF THE INVENTION

The object of the invention is achieved with a layered system especiallyfor use in the microelectronic or microtechnology field, with anelectrically-activatable layer which has on a first layer side extendingover at least a part of the layer surface, a contact electrode connectedtherewith. On the second layer side of the layer at least in the layerregion of the first contact electrode a multiplicity of transistorfunctions are provided, whereby one of the ends of the respectivecontrollable current channels (controlled by current (I)), of therespective transistor functions is connected with the layer. Thus theelectrically-activatable layer has on the first layer side, a contactelectrode which at least extends over a part of the layer surface. It isadvantageous if this extends over an as wide as possible part of thislayer up to a complete coating of this first layer side.

On the second layer side of the electrically-activatable layer thelayered system of the invention is provided at least in the layer regionof the first contact electrode, with a plurality of transistorfunctions, preferably a multiplicity of transistor functions. One of theends of the respective controllable-current-feeding current channels isthen connected with the electrically-activatable layer. These featuresenable lateral limiting of the current carriers on the second layerside, namely, in the region of the respective current channel up to theelectrically-activatable layer so that the laterally-limited layerregion included between the contact electrode on the first layer sideand the respective contact location of the individual current channelcan be electrically activated. Through a multiplicity of transistorfunctions on the second layer side, a pattern of many laterally-limitedlayer regions each controllably-defined by means of the controlelectrodes of the transistor functions (source S, drain D, gate G) areenabled.

In particular, the electrical activation generates anelectroluminescence in the electrically-activatable layer. It is,however, possible alternatively by electrical activation of the layer toexcite fluorescence to enable read-out of photodiodes to generate localchemical deposition, or to produce localized effects, for example, fromporosity superlattices. The system of the invention is not limited tothe electrical activation of an electroluminescence.

Advantageously, the plurality of transistor functions is provided as atransistor array in the layered system. In this manner a systematicarrangement of the transistor functions can be achieved on the secondlayer side of the electrically-activated layer.

A plurality of transistor functions can be provided at least by atransistor with a perpendicular current channel. It is, in this case,advantageous to provide the transistor as a permeable base transistor oras a heterobipolar transistor as is known, for example, from MaterialsScience and Engineering, B12 (1992), pages 156-160.

The layered system of the invention is especially advantageous when theelectrically-activatable layer extends as a large-area electrode over aplurality of transistor functions and it forms one of the controlelectrodes, be it the drain or the source, for the respective transistorfunctions.

At least in part the respective opposite end of the current channels canbe provided with a further electrically-activatable layer connected withthese channels. In this manner a layer system is achieved with a definedlateral electrical activation of one layer in a mirror-reversedpatterning of the pattern of the electrically-activated further layerdeposed on the opposite side.

A preferred embodiment of the layered system of the invention providesthat the material for the electrically-activated layer is a materialwith electroluminescent characterization. It can be advantageously aporous silicon. Further materials having a nanocrystalline structurewith electroluminescent characteristics are not, however, excluded.

In an advantageous manner the layered system of the invention isprovided on the first layered side with a contact electrode which is anelectrolytic contact electrode. By use of an electrolyte as a contactelectrode, in a known manner, the electrical activation in the case ofelectroluminescence can be advantageously an unclouded light emissionfrom the first layer side of the electrically-activated layer. With useof an electrolyte as one such counter electrode, it is possible inaddition to enable a defined local chemical precipitation from theliquid electrolyte.

In an embodiment of the invention the control electrode has a gate (G)function which is provided as a gridlike layer structure. This gridlikelayer structure can be configured of a sieve shape or another shape.Such a structure as the control electrode enables the second of therespective space charge zones in several current channelssimultaneously. By application of a blocking potential, the space chargezones constrict the respective current channels. In the conductiondirection, the space charge zones are reduced to the extent that acurrent of charge carriers is enabled to flow through the currentchannel. Usually the charge carrier on the transport is an electrontransport, although it can also involve a hole transport.

An embodiment of the invention can have the gridlike layer structureformed from two layers which are located at different distances from thelayer side of the electrically-activatable layer. These two layerssubstantially parallel to the layer side of the electrically-activatablelayer are provided with lateral fingerlike structures. With a mutuallyorthogonal orientation of these structures, they form in their totalitya matrix of mutually parallel current channels as a current channelmatrix whereby in an especially advantageous manner the elements ofthese two layers individually are provided as controllable fingerelements with current channels individually controllable within thegridlike layer structure. As a result, with the aid of a plurality ofsuch laterally-bounded adjustable electrical activations in theelectrically-activatable layer, an optionally definable activationpattern can be produced. It is conceivable in the case of use of theelectrical activation in the form of an electroluminescence to use sucha layer system for generating images on the first layer side of theelectrically-activatable layer so that the images of such a layer systemwith an electrically-activatable layer can be television picture screensor comparable imaging devices.

For the case that at least the layer of the gate (G) closest to theelectrical activation layer is so close to the electrical activationlayer that the space charge zones extend to the second layer side, onehas an especially advantageous embodiment of the claimed invention. Withthis feature, a widening of the current channel in the direction of thesecond layer side of the electrically-activated layer can be controlledwith reduction to avoidance of such enlargement. Without limitation,alternatively instead of the latter, a predetermined doping of thematerial current channel can be provided which, in the direction of thesecond layer side has diminished or decreasing doping to reduce thespread of the current channel in this region. In both cases it canadvantageously be achieved that a laterally-limited defined activationof the active layer is effected in a yet smaller lateral region which,with a multiplicity of transistor functions, gives rise to an improvedresolution of the electrical activation pattern.

Finally it can be advantageous to configure the layered system of theinvention so that as the electrically-activatable layer, a quantum dotarray is provided.

To the extent that an electroluminescence is achieved in theelectrically-activated layer, with the layered system of the inventionand even with those which utilize a contact electrode in the form of anelectrolyte, inexpensively produced large area light arrays can beformed. No subsequent structuring of porous silicon then is required.

The layered system of the invention can be fabricated in silicon orgallium arsenide technology. Thus the control electrodes of therespective transistor functions can be fabricated from metal or metallicsuicides or even contra-doped materials. With gates as the controlelectrode, a Schottky or also a PN junction can be provided. It ispossible, as material for the source-control electrode, to producehighly doped semiconductive material, especially of a gallium arsenideor also a silicon basis.

The invention layer system can be constructed from anelectrically-activatable layer of electroluminescing AlGaAs--GaAs oralso of semiconductive β-FeSi₂ so that, with the aid of the transistorarrays, locally controlled, these layers can form lamps with photodiodefunctions. As further functions which can be locally effected at theelectrically-activatable layer, local fabrication of porous silicon canbe considered which advantageously form porosity superlattices. In totalthis results in a layered system according to the invention whichenables materials, with advantageously large-area contacts, to beelectrically locally controlled, preferably with the aid of atwo-dimensional transistor array. This transistor array is located belowthe material and can be fabricated before the application of thematerial. It permits an epitactic, monocrystalline application offurther layers, (e.g. silicon for the production of porous silicon). Thetransistor array can be controlled through lateral terminals in a columnmanner and/or a row manner. A control logic can be integrated withoutproblems on the semiconductor chip. The process is very simple from theconcept on and can be carried out by standard prevalent technologicalsteps. As a whole it provides with the layered system of the invention athree-dimensional integration in the realm of microelectronics.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIG. 1 is a perspective view of the layered system of the invention,with a large area electrode as active layer and contact electrode withtwo electrode grids, one of which is provided for the transistorfunctions;

FIG. 2a is a plan view a gridlike layered structure as the gate withinthe layered system of the invention, comprised of two strip grid layersgrid 1 and grid 2;

FIG. 2b is a cross section through the layered system of the inventionaccording to FIG. 1 and FIG. 2a;

FIG. 3a is a plan view; and FIG. 3b is a cross section diagrammaticallyspace charge zones in the region of the gate control electrode in thelayered system of the invention;

FIG. 4 is a perspective view of the layered system of the invention withthe drain and source as large-area electrically active layers boundingthe layered system;

FIGS. 5a-d show the sequence in fabrication of the layered system of theinvention.

In FIG. 1, the layered system of the invention is shown in perspectiveview with a large-area electrode of an active layer 1 and contactelectrode 3 not shown in detail. Further indicated in FIG. 1 is agridlike control electrode of two individual layers 55 or 56 with thestriplike elements 57, 58, 59 or 67, 68, 69, designated as grid 2 orgrid 1 in the Figure. The layers 55 and 56 are at different spacingsfrom the electrically-activatable layer 1 and are oriented mutuallyperpendicularly to one another. Thus they form a matrix of mutuallysubstantially parallel individually elements 57, 58, 59, 67, 68 or 69,as required, individually controllable current channels controlled bythe elements 57-59 and 67-69. Each individually controllable currentchannel enables a laterally highly limited activation of the layer 1 sothat the totality of such current channels or multiplicity of suchcurrent channels or transistor functions enables the setting of anactivation pattern in the layer 1 depending upon the scanning orboundary conditions.

FIG. 2a shows schematically a gridlike layer structure with the aid oftwo layers 55 and 56 of which the striplike elements of the fingerformed layers 55 and 56 are visible from above. Between the individualstrips there are formed individual current channels as a consequence ofthe orthogonal arrangement of the grid 1 to the grid 2 forming a matrixof openings in space defining the individual current channels.

A cross section of the layered system of the invention perpendicular tothe layer orientation is shown in FIG. 2b. It is formed from top tobottom of a contact electrode 3 in the form of an electrolyte, theelectrically-activatable layer 1, here a large-area electrode of poroussilicon with a drain function. Therebelow and of a base of silicon, is aPBT with a gridlike gate (in the sense of the grid 2 of FIG. 2a) withthe individual strip elements 57, 58, 59 . . . surrounded by spacecharge zones 47, 48, 49. . . . On the underside as a source, the grid 1is provided orthogonal to the grid 2. In the schematic illustration ofFIG. 2b, the space zones as a result of suitably applied blockingvoltages are so formed that a charge carrier current I between the stripelements 47, 48, 49, cannot pass to the porous silicon so that anactivation, depending upon the choice of the porous silicon as anactivatable layer, through electroluminescence with light emission inthe layer 1 does not occur.

In FIG. 3a, the gridlike structure has one of its strip elements, inthis Figure designated at G2n and a strip element orthogonal thereto andindependently controllable at G1m individually controlled so that withinthe matrix of the current channels individually selected currentchannels are switched to be current-conducting or currentless. In FIG.3b a vertical section through this system is shown. The space chargezones around the middle strip elements are so constructed by suitablecontrol that a charge carrier current I can pass through the currentchannels 25 or 26 from the source S, through the striplike layer G2 ofthe active layer 1 here indicated as a drain D. With the aid of acontact electrode 3 not separately illustrated in this schematicshowing, on the upper side of the active layer 1, in the region of theengagement of the current channels 25, 26 with the layer 1, a region ofthis layer (here indicated by wide hatching) and laterally-limited, isactivated.

FIG. 4 shows the layered system of the invention in which theelectrically-active layers 1 and 31 bounding the two sides of thelayered system are formed as drain and source. Neither in this or in theother Figures is each individual transfer function indicated bydetailing the materials used.

The sequence in fabricating the layered system of the invention isschematically illustrated in FIGS. 5a-d. On the semi-insulatingsubstrate with the aid of an N⁻ implantation, a first fingerlike layeris formed in the undoped silicon substrate with the aid of a strip mask.Thereafter by annealing any implantation defects are healed (FIG. 5a).

In a further step an N⁻ layer is applied on the N⁺ layer (FIG. 5b). TheN⁺ layer is thus formed as a grid 1. With the aid of a cobalt-highdosage-ion implantation, using a suitable strip mask, a furtherfingerlike structure, here as grid 2, is formed. The grid 2 actsfunctionally as a metallically-conducting gate control electrode buriedin the N⁻ epitactic layer. The strip configuration of the grid 2 isorthogonal to the strip configuration of the grid 1 (FIG. 5c). Toproduce the monocrystalline buried cobalt silicide, a brief annealing isrequired. Then further N⁻ epitaxy is effected. In a known manner poroussilicon is finally applied to the prior structure with transistorfunctions. It is self-understood that here, although not shown indetail, that upon the porous silicon layer a further contact electrodecan be provided. In the case of utilization of electroluminescentcharacteristics of the material of the selected active layer, a liquidelectrolyte can be used as a contact electrode on top of the previouslyproduced layer system. Drain, source and gate of the layered system ofthe invention can be obtained by suitable choice of the conductivitycharacteristics depending upon the desired boundary conditions and canbe individually controllable.

We claim:
 1. An electronic component comprising:a body of asemi-insulating material capable of forming current channels therein; anelectroluminescent electrically activatable layer of porous silicon onsaid body; a electrically conductive layer on said electricallyactivatable layer and forming a transistor-function drain; a first gridburied in said body and formed by a coplanar array of mutually parallelconductors; a second grid buried in said body and formed by a coplanararray of mutually parallel conductors spaced between said first grid andsaid electrically activatable layer and orthogonal to the conductors ofthe first grid; another electrically conductive layer on said bodyforming a transistor-function source; and means for independentlyenergizing the conductors of said first grid and the conductors of saidsecond grid whereby a multiplicity of separately controllable transistorfunctions are formed by said grids in the form of respective permeablebase bipolar transistors or heterobipolar transistors creatingcontrollable current channels from said source to said drain throughsaid electrically activatable layer, thereby activating same.
 2. Thecomponent defined in claim 1 further comprising another electricallyactivatable layer on said body activatable by said current channels. 3.The component defined in claim 1 wherein the porous silicon has amonocrystalline structure.
 4. The component defined in claim 1 whereinsaid electrically conductive layer is a layer of an electrolyte.
 5. Thecomponent defined in claim 1 wherein said second grid is disposedsufficiently close to said electrically activatable layer that spacecharge zones of said second grid reach said electrically activatablelayer.
 6. The component defined in claim 1 wherein said electricallyactivatable layer is provided as a quantum dot array.